Flashlight foolishness

A couple of months ago I had an idea for a very compact but efficient
pocket flashlight. The idea was to use an offset-fed parabolic
reflector (like satellite TV) rather than the traditional flashlight
design. Computer models indicated it would work well. Then I got
sidetracked on other things.
I've revisited that with a quick 'n dirty experiment. It seems to
work on the bench as well as in the 'puter.
More at
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Reply to
Don Foreman
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IIRC the military uses some LED flashlights with the LED mounted 'backwards' into a reflector because the beam is so much tighted so it gets less backscatter in a dusty environment.
Reply to
Nick Hull
Very interesting, Don. Thanks for sharing.
Bob Swinney
Reply to
Robert Swinney
That might be the Pelican Recoil.
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Similar idea, but this requires a fairly large reflector so the 3/8" dia body of the LED and its support structure don't present significant obscuration.
I believe Ian Stirling is/was contemplating this configuration using a sapphire lens as both support and heatsink.
Reply to
Don Foreman
Perhaps I'm missing something, but aren't you going to lose a lot of optical efficiency with an offset feed unless you perform a somewhat difficult change in the shape of the reflector to compensate for off-axis illumination?
Since you have a computer, run a simple ray-tracing program and see what the results are.
Harry C.
Reply to
hhc314
No. Perhaps "offset feed" was misleading. "Assymetrical feed" might have been better terminology. The light source is still at the focal point of a paraboloid. Since the Luxeon is not omnidirectional (as a lightbulb is), I'm simply orienting it to maximize the amount of its light that hits the reflector rather than going forward without hitting the reflector, and eliminating unused portions of what would otherwise be a full paraboloid to get a low profile.
Satellite TV antennae work the same way; the dishes are sections of a paraboloid with the pickup head positioned so it doesn't obscure the dish's "view".
Did that with MathCAD, got an intensity plot. The real-life spot on the wall looks very similar to the simulation results.
Reply to
Don Foreman
I am, I'm wondering at the moment if extracted dies from luxeon stars is indeed the best way.
Reply to
Ian Stirling
In the USA the first version of this light was the Stealthlite 2020 or something like that. It had a great beam that was almost square like the die of the LED itself. Scatter was almost nothing at all. The only flahslight I have with a beam nearly as tight is a Maxabeam.
The one I had had a screw to operate switch and was total garbage. They changed the materials used, but it was still poor. It was hard to turn on and off, or would turn on an off itself. There was never a clear separation between on and off either.
Pelican needs to come up with a better switch system. Toggles that don't lock on or off without a peg that breaks off is stupid.
D> >>
Reply to
Crow Leader
Keep us posted, Ian! I use emitters rather than Stars, but extracting the die would be well beyond my ability. I figure the die is about 1 mm square while the emitter body is about 8 mm dia, so you'd gain a little if you could do that. How much you'd gain would depend on the reflector diameter.
Streamlight gets good results from batwing Luxeons in their very deep short-focus reflectors. A batwing might be a good choice for a retro.
Reply to
Don Foreman
something like that. It had a great beam that was almost square like the die of the LED itself. Scatter was almost nothing at all. The only flahslight I have with a beam nearly as tight is a Maxabeam.
the materials used, but it was still poor. It was hard to turn on and off, or would turn on an off itself. There was never a clear separation between on and off either.
on or off without a peg that breaks off is stupid.
Good small switches are hard to find unless you're buying in production qty. I'm using magnetic reed switches. They're very small, very reliable and hermetically sealed.
I think the assymetrically-fed (was "offset fed") paraboloid would match the retro's beam tightness by simply blacking out the portion of the Luxeon that can "see" directly out the reflector's aperture so that *all* light is collimated. The loss that would produce is probably less than the blockage presented by the emitter and support structure in a retro design.
A little "spill" is generally not a bad thing in a flashlight. Don't need or want much, just enough to see one's feet and immediate (arm's length) surroundings and direct the rest where it's needed at greater distance. A totally contained beam is only necessary if one is concerned about backscatter in fog or very dusty condx. Tactical users may also be concerned about ability of a distant off-axis observer to localize the light -- and therefore it's user. (Think target) In fog, rain, snow, dust, buggy or even humid condx the beam will draw a line to the user anyway so the only real advantage is freedom from being blinded by backscatter.
Reply to
Don Foreman
That form factor looks like it would work well attached to a headband.
-- Regards, Carl Ijames carl.ijames at verizon.net
Reply to
Carl Ijames
On Fri, 04 Mar 2005 02:41:19 GMT, the inscrutable "Carl Ijames" spake:
But with the battery on the back of the band, balancing the weight, perhaps?
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Reply to
Larry Jaques
something like that. It had a great beam that was almost square like the die of the LED itself. Scatter was almost nothing at all. The only flahslight I have with a beam nearly as tight is a Maxabeam.
changed the materials used, but it was still poor. It was hard to turn on and off, or would turn on an off itself. There was never a clear separation between on and off either.
on or off without a peg that breaks off is stupid.
They make enough flashlights to tool up to make all those plastic parts. I like their toggle switch except for the fact you cannot lock it on or off without the peg. They should add an internal spring so it snaps on or off, like a normal rocker switch. Their service has been awful in the past year or so, so I'm off to new vendors now.
Reply to
Crow Leader
I'd like the total diameter of the light to be about 17mm or so, with a 14mm or so clear apature. 8mm is really annoying in this case. However, getting it to 5 is pretty easy. I'm also investigating other ways.
Reply to
Ian Stirling

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